James M Snell wrote:
IOW, using the XHTML2 div as the child is compliant in a strictly sense but should be avoided because it will likely cause problems.
An XHTML2 div is not compliant. The normative reference is to XHTML Modularization, and the accompanying XHTML1 definitions and namespace. In practice, this requirement is somewhat malleable, since XHTML's DTD requires that all elements reside in the default namespace (a flaw in XHTML), and XHTML Modularization makes some other universally-ignored requirements.
XHTML2's namespace is different, though there is an open issue to change to the same namespace that XHTML1 uses. Even if the namespace were the same, Atom processors are not required expected to understand or comply with any XHTML[2] markup.
In other words, Atom processors will pick up (X)HTML features as they see fit. The spec is quite specific on this point (using the markup is a MAY). In practice, (X)HTML support and security varies widely.
-Rob
